1. Field of the Invention
The present invention relates generally to electrical switch apparatus and in particular to a multiplex switch system which may be used in combination with existing conductors for transmitting information to be used for the control of a remote operation.
2. Description of the Prior Art
Many advanced electronic devices, such as calculators, require digital displays as well as complex data inputs through keyboard or other types of switches. Because the cost of the integrated circuit bears a direct relationship to the physical size of the integrated circuit, means have been developed for sharing lines to serve both the function of driving the digital display elements and interrogating the keyboard. These techniques have been limited in the past to displays such as the light emitting diode (LED) variety which operate from direct current and which are digit-by-digit multiplexable. Similar sharing techniques have not been available for use with displays requiring continuous alternating current drive, such as the liquid crystal display (LCD). Although the LCD displays require continuous drive on all segments they generally have relatively slow response, typically on the order of a few hundredths of a second to change from dark to light or light to dark.
Therefore, it is the principal object of the present invention to provide a multiplex switching system which can be combined with existing conductors which drive visual display elements of an LCD digital data display system for indicating the setting of a movable switch element such as a touch pad of a keyboard.
There are a number of important applications in which it is desirable to input a large amount of information through a slide bar type switch into an electrical circuit such as an integrated circuit of a microprocessor. An example of such an application is a digital electronic thermostatic controller for home, office and business air conditioning and heating control applications. Such a thermostatic control requires a large number of data inputs including selection of temperature over a 40.degree. to 50.degree. temperature range. This information can be fed into a thermostatic controller in digital form with a keyboard input device, but to gain broad market acceptance, minimize setting errors and have all the settings apparent or "intuitively obvious" at all times, an analog or "sliding bar" type of input is desirable. With such an arrangement, less operator training is required, less reliance on instruction manuals is needed, and in business applications, the settings can be determined through a clear plastic cover which may be locked over the thermostat control unit to prevent tampering.
However, with a conventional sliding bar type of input arrangement, to bring out the large number of conductors necessary for encoding the position of the sliding bar switches would mean that the integrated circuit receiving the inputs would necessarily require an inordinately large capacity to be compatible with the required number of data input nodes. Therefore for domestic applications where minimum size and aesthetic appearance are important considerations, it has not been practical to implement the conventional sliding bar type arrangement, even though it provides the aesthetically pleasing, intuitively obvious indication of input setting.
Therefore, it is a principal object of the invention to provide the switching system for use in combination with an LCD data display devices which utilizes a sliding bar or movable switching element in combination with an array of conductors for intuitively indicating the setting of the switch within a given range and capable of providing resolution within the range which does not require a large number of additional conductors.
A further object of the invention is to provide a multiplex switching system which can be combined with existing conductors which drive visual display elements of an LCD digital data display system for indicating the actuation of a movable switch element of a touch pad keyboard.
It is yet another object of the invention to provide an electrical switch capable of inputting a large amount of data and which involves a minimal number of parts that are capable of compact arrangement.